Tuning the photophysical properties of N^N Pt(ii) bisacetylide complexes with fluorene moiety and its applications for triplet–triplet-annihilation based upconversion
作者:Qiuting Li、Huimin Guo、Lihua Ma、Wanhua Wu、Yifan Liu、Jianzhang Zhao
DOI:10.1039/c2jm15678d
日期:——
Fluorene-containing aryl acetylide ligands were used to prepare N^NPt(II) bisacetylide complexes, where aryl substituents on the fluorene are phenyl (Pt-1), naphthal (Pt-2), anthranyl (Pt-3), pyrenyl (Pt-4), 4-diphenylaminophenyl (Pt-5) and 9,9-di-n-octylfluorene (Pt-6) (where N^N ligand = 4,4â²-di-tert-butyl-2,2â²-bipyridine, dbbpy). All the complexes show room temperature (RT) phosphorescence. The emissive T1 excited states of Pt-1, Pt-5 and Pt-6 were assigned as metal-to-ligand-charge-transfer state (3MLCT), whereas for Pt-2, Pt-3 and Pt-4, the emissive T1 excited states were identified as the intraligand state (3IL), based on steady state emission spectra, the lifetime of the T1 state, emission spectra at 77 K, spin density analysis and the time-resolved transient absorption spectroscopy. Exceptionally long lived T1 excited state was observed for Pt-3 (Ï = 66.7 μs) and Pt-4 (Ï = 54.7 μs), compared to a model complex dbbpy Pt(II) Bisphenylacetylide (Ï = 1.25 μs). RT phosphorescence of anthracene was observed at 780 nm with Pt-3. The critical role of the fluorene is to move the absorption of the complexes to the red-end of the spectra, but at the same time, without compromising the energy level of the T1 state of the complexes. The advantage of this unique spectral tuning effect and the long-lived T1 excited states of Pt-4 was demonstrated by the enhanced performance of the complexes as triplet sensitizers for tripletâtriplet annihilation (TTA) based upconversion; an upconversion quantum yield (ΦUC) up to 22.4% was observed with Pt-4 as the sensitizer. Other complexes described herein show negligible upconversion. The high upconversion quantum yield of Pt-4 is attributed to its intense absorption of visible light and long-lived T1 excited state. Based on the result of Pt-4, we propose that weakly phosphorescent, or non-phosphorescent transition metal complexes can be used as triplet sensitizers for TTA upconversion, compared to the phosphorescent triplet sensitizers currently used for TTA upconversion. Our results will be useful for the design of transition metal complexes to enhance the light-absorption and thereafter the cascade photophysical processes, without decreasing the T1 excited state energy levels, which are important for the application of the complexes as triplet sensitizers in various photophysical processes.
含氟苯的芳香烃乙炔配体被用于制备N^NPt(II)双乙炔配合物,其中氟苯上的芳香取代基为酚基(Pt-1)、萘基(Pt-2)、蒽基(Pt-3)、芘基(Pt-4)、4-二苯胺苯基(Pt-5)和9,9-二正辛基氟苯(Pt-6)(其中N^N配体为4,4' -二叔丁基-2,2' -联吡啶,dbbpy)。所有配合物在室温下均显示出磷光。通过稳态发射光谱、T1态的寿命、77K下的发射光谱、自旋密度分析和时间分辨瞬态吸收光谱法,将Pt-1、Pt-5和Pt-6的发射性T1激发态归类为金属-配体电荷转移态(3MLCT),而Pt-2、Pt-3和Pt-4的发射性T1激发态则被鉴定为配体内态(3IL)。Pt-3(τ = 66.7μs)和Pt-4(τ = 54.7μs)显示出异常长寿命的T1激发态,相较于模型配合物dbbpy Pt(II)双苯乙炔(τ = 1.25μs)。观察到Pt-3在780nm处有蒽的室温磷光。氟苯的关键作用是将配合物的吸收移至光谱的红端,同时不降低配合物T1态的能级。这种独特的光谱调谐效应以及Pt-4的长寿命T1激发态的优势,通过配合物在三重态-三重态湮灭(TTA)基础上的上转换作为三重态敏化剂的增强性能得以体现;观察到Pt-4作为敏化剂的上转换量子产率(ΦUC)高达22.4%。其他在此描述的配合物几乎没有上转换。Pt-4高上转换量子产率的原因在于其对可见光的强吸收和长寿命的T1激发态。基于Pt-4的结果,我们提出弱磷光或非磷光的过渡金属配合物可以用作TTA上转换的三重态敏化剂,相较于目前用于TTA上转换的磷光三重态敏化剂。我们的结果将有助于设计过渡金属配合物,以增强光吸收及其后的级联光物理过程,同时不降低T1激发态能级,这对这些配合物在各种光物理过程中的应用作为三重态敏化剂至关重要。